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                [Shoi2016]随机序列                </h1>
                <p>时间限制：20s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><div>
<div>
<div>你的面前有N个数排成一行。分别为A1, A2, &hellip; , An。你打算在每相邻的两个 Ai和 Ai+1 间都插入一个加号或者</div>
<div>减号或者乘号。那么一共有 3^(n-1) 种可能的表达式。你对所有可能的表达式的值的和非常感兴趣。但这毕竟太</div>
<div>简单了，所以你还打算支持一个修改操作，可以修改某个Ai 的值。你能够编写一个程序对每个修改都输出修改完</div>
<div>之后所有可能表达式的和吗？注意，修改是永久的，也就是说每次修改都是在上一次修改的基础上进行， 而不是</div>
<div>在最初的表达式上进行。</div>
</div>
</div>
<p></p></p><hr/><h3>输入格式</h3><p><div>第一行包含 2 个正整数 N 和 Q，为数的个数和询问的个数。</div>
<div>接下来一行 n 个非负整数，依次表示a1,a2...an</div>
<div>在接下来 Q 行，其中第 ?? 行两个非负整数Ti 和Vi，表示要将 A<sub>ti</sub> 修改为 Vi。其中 1 &le; Ti &le; N。</div>
<div>保证对于 1 &le; J &le; N, 1 &le; i&le; Q，都有 Aj,Vi &le; 10^4。</div>
<div>N,Q&lt;=100000,本题仅有三组数据</div>
<p></p></p><hr/><h3>输出格式</h3><p><div>输出共 Q 行，其中第 i 行表示第 i 个询问之后所有可能表达式的和，对10^9 + 7 取模。</div>
<p></p></p><hr/><h3>样例输入</h3><pre>5 5
9384 887 2778 6916 7794
2 8336
5 493
3 1422
1 28
4 60
</pre><hr/><h3>样例输出</h3><pre>890543652
252923708
942282590
228728040
608998099</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>By 佚名上传</p>
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